Two-stage pump with high head and low delivery

ABSTRACT

Pump comprising a body ( 10 ), an actuating shaft ( 1 ) on which at least a first impeller ( 21   a ) and a second impeller ( 21   b ) are coaxially mounted, each being housed in a respective front chamber ( 15   a ) and rear chamber ( 15   b ) respectively connected to a fluid intake duct ( 11 ) and a fluid delivery duct ( 13 ), in which said front chamber ( 15   a ) is delimited by said body ( 10 ) and by an interstage body ( 16 ), said rear chamber ( 15   b ) is delimited by said interstage body ( 16 ) and by a shield ( 23 ), said interstage body has two volutes ( 22   a   , 22   b ) respectively associated with the corresponding first impeller ( 21   a ) and second impeller ( 21   b ), a first discharge orifice ( 16   a ) connecting the volute ( 22   a ) of the first impeller ( 21   a ) to the exterior, a second discharge orifice ( 16   c ) connecting the volute ( 22   b ) of the second impeller ( 21   b ) to the delivery duct ( 13 ), inside said body ( 10 ) there being formed a channel ( 17 ) for the throughflow of the fluid from said first chamber ( 15   a ) to the means for supplying the fluid to the second impeller ( 21   b ).

[0001] The present invention relates to a two-stage pump with a highhead and low delivery.

[0002] In the sector in question particular types of pump (called PEP,i.e. Partial Emission Pumps) are known, said pumps having thecharacteristics of a high head and low delivery and being of the typewhere a fluid, contained in a tank and subject to the pressuredetermined by the fluid column, enters into the pump in an axialdirection and is pushed by the impeller towards the delivery ductarranged in a tangential direction and having dimensions such as todetermine the required head of the pump.

[0003] It is also known that, in order to be able to increase the headof the pump, it is possible to modify only the number of revolutions ofthe impeller which, consequently, must be designed with a special formable to ensure that the inlet pressure is maintained; otherwise, theincrease in the number of revolutions would result in a reduction in theinlet pressure and consequently a reduced intake of fluid with aconsequent decrease in the efficiency of the pump; this effect is evenmore marked in those cases where the pump is arranged at a level higherthan that of the free surface of the fluid to be drawn.

[0004] In order to overcome this drawback, high-speed pumps have beendesigned, of the type provided with a fast main impeller able toincrease substantially the head and an auxiliary impeller arrangedupstream of the first impeller and able to supply the main impellerwithout a substantial loss in suction of the fluid at the inlet andwithout affecting the increase in the delivery pressure of the pump.

[0005] These pumps, however, are complicated and costly to manufactureand moreover require special parts with a limited degree ofstandardization.

[0006] The technical problem which is posed, therefore, is that ofdesigning pumps which are able to operate within a wide range of lowdelivery values and with a high head, without being affected by theabovementioned problems of the existing art.

[0007] Within the context of this problem a further requirement is thatthe pump should have compact dimensions and have high interchangeabilitycharacteristics, namely should allow variation in the rated deliverywithin a wide range of operating values, with minimum modificationswhich do not involve the general structure of the pump and allow thelargest possible number of components to be standardized, reducing inthis way the storage requirements and consequently the production andmanagement costs.

[0008] These results are obtained according to the present invention bya pump comprising a body, an actuating shaft, on which at least a firstimpeller and a second impeller are coaxially mounted, each being housedin a respective front chamber and rear chamber respectively connected toa fluid intake duct and a fluid delivery duct, in which said frontchamber is delimited by said body and by an interstage body, said rearchamber is delimited by said interstage body and by a shield, saidinterstage body has two volutes respectively associated with thecorresponding first impeller and second impeller, a first dischargeorifice connecting the volute of the first impeller to the exterior, asecond discharge orifice connecting the volute of the second impeller tothe delivery duct, inside said body there being formed a channel for thethroughflow of the fluid from said first chamber to the means forsupplying the fluid to the second impeller.

[0009] Further details may be obtained from the following description ofa non-limiting example of embodiment of the subject of the presentinvention provided with reference to the accompanying drawings, inwhich:

[0010]FIG. 1 shows a partially sectioned schematic perspective view ofthe pump according to the present invention;

[0011]FIG. 2 shows a partially sectioned schematic perspective view ofthe pump according to FIG. 1;

[0012]FIG. 3 shows a schematic cross-section through the pump accordingto FIG. 1.

[0013] As shown in FIG. 1, the pump according to the present inventioncomprises a body 10 with which the duct 11 for axial entry of the fluidis associated; said duct 11 is formed inside a coaxial extension 12provided with a flange 12 a for frontal coupling with the supplyapparatus.

[0014] For the sake of convenience of description said partcorresponding to the body 10 of the pump and to the fluid inlet will bedefined below as “front”, while the opposite side will be defined as“rear”.

[0015] Said front body 10 also contains the fluid delivery duct 13 whichextends in a direction tangential to the said body 10 inside acorresponding extension 14 with which an associated coupling flange 14 ais integral.

[0016] A suitable annular seat 15 is formed in the body 10 and has,arranged therein, a coaxial interstage body 16 through which the pumpactuating shaft 1 passes via a bush la.

[0017] Said interstage body 16 essentially divides the annular seat 15into a first front chamber 15 a and into a second rear chamber 15 b;inside these chambers a first impeller 21 a and a second impeller 21 brespectively rotate, being both mounted on the said actuating shaft 1;said impellers are identical, symmetrical and opposite to each other.

[0018] Said chambers 15 a, l5 b communicate with the exterior by meansof respective volutes 22 a and 22 b which, in a preferred embodiment,are of the annular type, have a constant cross-section and havedischarge nozzles 16 a, 16 b which are angularly offset at 180° withrespect to each other.

[0019] Said second chamber 15 b is closed at the rear and axially closedby a shield 23 inside which (FIGS. 2 and 3) a radial duct 24 is formed;one external end 24 bof said duct is connected to a channel 17 which isparallel to the longitudinal axis of the pump and formed in the frontbody 10 thereof and the other internal end 24 a is connected to acoaxial annular header 25 which emerges coaxially in said rear chamber15 b.

[0020] The front chamber 15 a is connected to the said axial duct 17 ofthe body 10 by means of a volute 22 a, the said discharge nozzle 16 aformed in the interstage body 16 and arranged in a tangential direction,and a radial duct 16 c; the rear chamber 15 b is in turn connected tothe tangential delivery duct 13 by means of the volute 22 b, theassociated discharge nozzle 16 c formed in a tangential direction in theinterstage body 16 and a corresponding radial duct 16 d formed in thebody 10 of the pump.

[0021] The shield 23 also has a coaxially extending seat 23 a in whichit is possible to mount all the sealing devices on the shaft, wherebythe possibility of installing magnetic-coupling drive devices necessaryfor highly dangerous, radioactive and similar fluids is also envisaged.

[0022] The pump is closed at the rear by a casing 30 acted on by aflange 31 which ensures clamping of the shield 23 and the interstagebody 16 in the axial direction.

[0023] The supports 40 of the shaft 1 are fastened on the other side ofthe casing 30. Said parts of the pump are conventional per se andtherefore not described in detail.

[0024] The operating principle of the pump is as follows:

[0025] the fluid which enters via the intake duct 11 reaches the firstchamber 15 a where it is subjected to the action of the first impeller21 a which pushes it into the volute 22 a and from here into the duct 16a, 16 b for connection to the channel 17 which emerges in the radialduct 24 of the shield 23;

[0026] along this first travel path the fluid undergoes the firstincrease in pressure with respect to the intake pressure;

[0027] upon leaving the radial duct 24 the fluid is forced inside theannular header 25 which arranges it in the axial direction for entryinto the second chamber 15 b where it is subjected to the action of thesecond impeller 21 b which forces it into the volute 22 b and from hereinto the radial duct 16 c,16 d and then into the delivery duct 13 with afurther increased pressure.

[0028] It is pointed out therefore how the two impellers and theassociated concentric volutes produce a series action on the fluid ableto increase its head (typical values of up to 200 m of liquid column)without an increase in the number of revolutions of the impellers andtherefore without a reduction in the intake characteristics of the pumpwhich may continue operating close to the point of maximum efficiencywith advantages in terms of energy and fluid dynamics.

[0029] In addition to this, the pump according to the invention allows ahigh degree of interchangeability since it is possible to vary the rateddelivery of the pump (typical values ranging from 1 to 18 m³/h) bysimply changing the interstage body 16 and keeping unchanged theconfiguration and the dimensions of the other parts of the pump, whichalso has a rotating part which, owing to the symmetry and oppositepositioning of the impellers and the arrangement of the nozzles of thetwo volutes at 180°, is substantially free from the effect of radialand/or axial loads with a consequent increased structural rigidity whichfavours the working life of the sealing parts and the parts subject towear, increasing the reliability of the pump.

[0030] The pump according to the invention has moreover an extremelycompact design among other things owing to the formation, inside thebody, of the duct connecting the two stages, avoiding the excessivelylarge dimensions resulting from the external connection channels of theconventional type.

[0031] It is pointed out moreover how the pump body 10 has aconfiguration of the housing in the form of a radially divided “barrel”with flanged intake and delivery openings having the function ofwithstanding the rated pressure and housing the two impellers and theinterstage body containing the two concentric volutes with respectivediffusion channels and the rear shield inside which the radialinterstage connection channel, the intake header and the chamber housingthe shaft sealing device are formed.

[0032] In a preferred embodiment it is envisaged that the seal betweenthe body 10 and the shield 23 and the seal between the zones subject tothe differential pressures of the first and second stage consist ofseals 50 of the spiralled metallic type, made on the one hand of steeland on the other hand of graphite and able also to take up any playresulting from the mating or thermal expansion and/or contraction of thevarious parts.

1. Pump comprising a body (10), an actuating shaft (1) on which at leasta first impeller (21 a) and a second impeller (21 b) are coaxiallymounted, each being housed in a respective front chamber (15 a) and rearchamber (15 b) respectively connected to a fluid intake duct (11) and afluid delivery duct (13), characterized in that: said front chamber (15a) is delimited by said body (10) and by an interstage body (16); saidrear chamber (15 b) is delimited by said interstage body (16) and by ashield (23) said interstage body has: two volutes (22 a, 22 b)respectively associated with the corresponding first impeller (21 a) andsecond impeller (21 b); a first discharge orifice (16 a) connecting thevolute (22 a) of the first impeller (21 a) to the exterior; a seconddischarge orifice (16 c) connecting the volute (22 b) of the secondimpeller (21 b) to the delivery duct (13); inside said body (10) therebeing formed a channel (17) for the throughflow of the fluid from saidfirst chamber (15 a) to the means for supplying the fluid to the secondimpeller (21 b).
 2. Pump according to claim 1, characterized in thatsaid channel (17) of the body (10) is arranged parallel to thelongitudinal axis of the pump.
 3. Pump according to claim 1,characterized in that said discharge orifices (16 a,16 c) of the volutes(22 a,22 b) are arranged in a tangential direction.
 4. Pump according toclaim 1, characterized in that said orifice (16 a) for connecting thefirst volute (22 a) to said channel (17) of the body (10) is connectedto a first radial duct (16 b) formed in the said body (10).
 5. Pumpaccording to claim 1, characterized in that said means for supplying thefluid to the second impeller (21 b) comprise a radial duct (24) insidethe rear closing shield (23), the opposite ends of said duct (24) beingrespectively connected to the channel (17) of the body (10) and to aheader (25) for supplying the fluid to the second chamber (15 b). 6.Pump according to claim 4, characterized in that said header (25)supplying the fluid to the second rear impeller (21 b) has a coaxiallyextending nozzle for supplying the fluid to the impeller in an axialdirection.
 7. Pump according to claim 1, characterized in that saiddischarge orifice (16 c) of the second volute (22 b) is connected to thefluid delivery duct (13) by means of a second radial duct (16 d) formedin the said pump body (10).
 8. Pump according to claim 1, characterizedin that said interstage body (16) is interchangeable.
 9. Pump accordingto claim 1, characterized in that the volutes (22 a, 22 b) are annular.10. Pump according to claim 1, characterized in that the volutes (22 a,22 b) have a constant width.
 11. Pump according to claim 1,characterized in that the discharge nozzles (25 a, 25 b) of the volutesare angularly offset at 180° with respect to each other.
 12. Pumpaccording to claim 1, characterized in that said impellers areidentical, symmetrical and opposite to each other.
 13. Pump according toclaim 1, characterized in that the seals between the interstage body(16) and the pump body (10) and between the rear shield (23) and thepump body (10) consist of seals (50) of the spiral type.
 14. Pumpaccording to claim 13, characterized in that said seals (50) are made ofsteel and graphite.